The past decade has witnessed increased study and analysis of conditioned inhibition (CI) to the point where the phenomenon has gained a firm empirical basis, and thus scientific acceptance. Despite this, our knowledge of CI has remained scant, particularly by comparison with our understanding of conditioned excitation. The overall objective of the planned research, therefore, is to elucidate the nature of CI through a determination of the factors and conditions which are critical to its development, maintenance, and extinction. In particular, the aims of the research are: (1) to evaluate variations within, and to make comparisons across, different procedures used to generate CI (e.g., explicitly unpaired, differential, Pavlovian CI, delay conditioning, and excitatory extinction); (2) to assess the role of excitation, as mediated either by background stimuli or by an explicit conditioned stimulus (CS), or as produced directly by the unconditioned stimulus (US), in fostering the development of CI; (3) to study the generality and retention of CI based on both aversive and appetitive USs, and to examine the representation of CI in memory; (4) to investigate different methods by which second-order CI may be established, and to assess its "functional autonomy" or dependence on the first-order CS; and (5) to evaluate the effectiveness of various "decorrelation" procedures in extinguishing CI, as well as ancillary means of either blocking or enhancing that extinction. For the most part, these assessments will be made in the context of CER (conditioned-emotional-response) training, but where appropriate and necessary, the research will be extended to appetitive conditioning. The orientation of the research is predominantly empirical in nature, and is designed to elaborate, or delimit, the operational rules (e.g., a negative correlation of the CS and US) prescribed for establishing CI. Within this framework, however, the applicability and generality of various interpretations of CI will be assessed, with the intent of sharpening and refining these interpretations or, if need be, developing a new interpretation.